1. Field of the Invention
The present invention relates to a method of fabricating a micro-needle array, and more particularly, to fabricating a micro-needle array for obtaining and injecting micro-fluidic samples by using micro-machining fabrication technologies.
2. Description of the Related Art
Recently, with advancements of the micro-electro mechanical system (MEMS) and micro-machining technologies, more attention is paid to micro-needles.
A micro-needle has a micrometer-level channel diameter, and is used in a variety of fields. For example, a micro-needle is used as an accurate cell injection/extraction needle in the field of cell-biology, or used as an injection/extraction head for chemicals or solutions in chemicals delivery systems or in micro-chemicals factories. In addition, since a small-sized needle reduces inconvenience and pain associated with injections, micro-needles are advantageous in injecting medication into patients.
FIGS. 1A to 1G show a method of fabricating a glass or a silicon micro-needle through isotropic etching. As shown in FIGS. 1A to 1G, the conventional micro-needle array fabrication method, first, an isotropic etching mask 11 is vapor-deposited on a glass or a silicon substrate 10, and a hole pattern 12 is formed through a lithography process. Next, a channel 13 is formed in the glass or silicon substrate 10 through Deep Reactive Ion Etching (DRIE), and the surface of the substrate 10 is coated so that the channel is not etched. Then, a shape 15 is formed for isotropic etching on the front surface, a pointed tip 16 like a needle is formed through BHF etching, HF etching, or HNA etching, and, finally, the metal 11 used for the mask is removed, thereby fabricating a micro-needle 17. FIG. 2 shows an image of micro-needles fabricated according to the above method.
FIGS. 3A to 3E show a micro-needle fabrication method using silicon. As shown in FIGS. 3A to 3E, in the micro-needle fabrication method, first, a trench 21 is formed on silicon 20 through DRIE, and a channel 22 is formed on the opposite side in the same way. Next, the whole silicon 23 is coated in order to protect structure from silicon etching solution. Subsequently, the coating mask on top of the silicon is removed, and a slant surface 24 is formed by using anisotropic etching. Finally, the slant surface 24 is etched by an appropriate depth, and the coating 23 is removed, thereby completing a micro-needle 25. FIG. 4 shows an image of a micro-needle fabricated according to the above described micro-needle fabrication method.
As above, a conventional micro-needle fabrication method uses DRIE to form micro-needle channels in the substrate, but DRIE as above has a limitation with respect to a ratio of channel diameter to channel length, i.e. an aspect ratio. A micro-needle is required in itself to have a diameter less than tens of μm, but limitations exist in fabricating a micro-needle that has such a short diameter and a long channel due to the characteristics of current semiconductor equipment. Generally, the maximum aspect ratio of a micro channel that can be fabricated through DRIE is approximately 1:10. However, a micro-channel is required to be hundreds of μm long for its use, but it is difficult to form a channel having a diameter less than 10 μm and a length of hundreds of μm with conventional DRIE.
In addition, the conventional method is incapable of forming a silicon oxide needle having a high aspect ratio and a channel which is surrounded with a silicon oxide body.